Jet engine fuel supply system



Jan. 27, 1953 w. c. TRAUTMAN ETAL 2,626,655

JET ENGINE FUEL SUPPLY SYSTEM Filed July 25, 1945 E? 35 Z': FZ-E-?: 3943 4240 INVENTOR.

W. O. TRAUTMAN BY A. A. MEDDOCK ATTORNEY Patented Jan. 27, 1953 JETENGINE FUEL SUPPLY SYSTEM Walter C. Trautman, Los Angeles, and Alvin A.Meddock, North Hollywood, Calif., assignors to Bendix AviationCorporation, South Bend, 11111., a corporation of Delaware ApplicationJuly 25, 1945, Serial No. 607,030

11 Claims. 1

This invention relates to fuel supply systems in which a liquid fuel issprayed from atomizing jets into an air stream to create a combustiblemixture and has particular application to the fuel system of a jetengine in which the fuel pump is driven by the engine.

A broad object of the invention is to insure delivery of fuel at highpressure to the jets at the time of starting to produce thoroughatomization and prompt ignition of the mixture.

Another object of the invention is to provide more positive starting ofjet engines.

Another object is to facilitate restarting of jet engines after ashutdown.

Still another object is to prevent flooding of jet engines at the timeof starting.

Other more specific objects and features will become apparent from thedetailed description to follow of a particular embodiment of theinvention.

As now developed, a common form of jet engine burns kerosene or otherfuel of low volatility by discharging the fuel at high pressure throughatomizing jets into an air stream to form a comhustible mixture which isignited by a spark plug or other known type of igniter. Furthermore, thefuel pressure is developed by a pump which is driven from the jetengine, and the engine is started by an electric starter capable ofaccelerating the rotor of the engine to a speed at which it isoperative.

Difficulty has been encountered in starting such engines because of thefact that fuel was frequently admitted to the jets before theenginedriven pump was rotating fast enough to develop an atomizingpressure. As a result, fuel was discharged through the jets withoutbeing atomized sufficiently to produce an ignitible mixture with theair, which fuel accumulated in liquid form within the engine until suchtime as the fuel pressure rose to the point where sufficient atomizationwas obtained to permit ignition. Thereafter, the excess fuel that hadaccumulated in the engine burned rapidly and abnormally, withobjectionable results both with respect to the engine structure and toobjects in the path of the flame discharged from the engine.Furthermore, sometimes the flooding of the engine prevented startproducethorough atomization of the first fuel.

discharged, and thereby promote prompt ignition. This result isaccomplished by the use of an accumulator which stores the fueldischarged by the pump during initial operation thereof at slow speed,in combination with an automatic valve that releases the stored fuelfrom the accumulator at high pressure to the atomizing jets when thethrottle valve is opened.

In the drawing:

Fig. 1 is a schematic diagram of a jet engine in combination with a fuelsupply system in accordance with the invention; and

Fig. 2 is a detailed view partly in section of the accumulator andautomatic valve structure em ployed in the system of Fig. 1.

Referring first to Fig. 1, there is disclosed schematically aconventional form of jet engine 10 which comprises a rotor shaft llhaving an impeller 12 on one end for compressing air for com bustion andhaving a gas turbine 13 on the other end which is driven by thedischarge gases. Air enters the forward end of the engine through anopening [4, is compressed by the impeller 12, and delivered to anannular manifold l5 from which it is discharged through a plurality oforifices it into the forward end of an annular combustion chamber '1. Asthe air enters the combustion chamber through the orifices I6, it ismixed with atomized liquid fuel discharged from a plurality of jets 18,which are supplied with fuel under pressure through a pipe l8, which inturn is normally supplied with fuel under pressure from a reservoir 20,through a suction pipe H, a pump 22, a check valve 23, and a throttlevalve 24. The mixture of air and atomized fuel may be initially ignitedby sparks from spark plugs 25 energized from a standard ignition circuit(not shown). The burning fuel is then discharged through the combustionchamber ll past the gas turbine l3 and out through a discharge passage26. For purposes of illustration, the rotor shaft H is shown coupled byspur gears 21 and 28 to the fuel pump 22 and is also coupled through thespur gear 21, a spur gear 29, and a clutch 30 to an electric startingmotor 3i.

It has been the practice to drain all fuel from the line I9 and the jetsI8 when the engine is shut down. To this end, a drain line H containinga drain valve 10 is extended from the line is back to the reservoir 20.As shown, the valve 10 contains a poppet '12 which is normally liftedoff its seatl3 by a light compression spring It, so that whenever thepressure in the line I9 drops to a low value following the closure ofthe throttle 24, the spring 14 lifts the poppet oil the seat 13 aeaaescescape of fuel through the drain line when the,

engine is operating. 7

The structure so far described is conventional and its normal operationhas been outlined. At the time of starting, a switch 32 in the startingcircuit of the motor Si is closed, causing the latter to engage theclutchciio and accelerate the rotor shaft it and the pump 22. Initially,it has been the practice to slightly open the throttle valve 24 topermit the minimum. flow from the jets it necessary to sustain operationof the engine, and theoretically the mixture should be ignited and theengine should start to operate as soon as the starting motor 3! hasaccelerated the impeller E2 to a speed at which it will deliver sumcientair for operation. Often, however, it has been found that during theinitial period of operation, the pump 22 was running too slowly to buildup any substantial pressure in the pipe iii, with the result that fuelwas discharged at low pressure from the jets l8 for a considerableinterval of time before ignition took place, this fuel accumulating inthe en ine so that if and when ignition did finally take place, therewas sufiicient accumulated fuel to cause abnormal combustion of a veryrich m xture that produced excessive heat within the tail portion of thejet engine itself and caused pro ection of flame to a substantialdistance beyond the en ine. until the excess accumulated fuel had beenconsumed. Furthermore, the flow of fuel from the jets 58 while the pump22 was coming u to speed prevented the fuel pressure from r sing asrapidly as it would if such initial flow from the jets were prevente andsometimes the pump was su plying insufficient pressure to roduceatomization at the time the im eller i2 has reached a sneed at which theengine would normally be operative. This prolonged the starting periodand sometimes exhausted the starting battery 33 which drives the start nmotor 3 i In accordance with the present invention the foregoing obectionable start ng characteristics have been eliminated or greatl mtigated y the provision of a valve and accumulator unit 35 having aninlet connection 36 connected to the fuel line ahead of the throttlevalve 245 and having an outlet connection Si connected to the fuel lineon the outlet side of the throttle valve.

Referring to Fig. 2, the unit 35 consists of an accumulator 35c and anautomatic valve 35b for controlling flow between the accumulator 35a andthe connections 36 and 3?. The accumulator 35c comprises a shell 38containing a bladder 8d, the neck dd of which is in sea-ling relation tothe shell at the bottom thereof. Thus, the lower end of the shell 38 maybe closed by a screw plug it which compresses an annular flanged member512 against the neck d8 of the bladder. The flanged member 412 containsholes 33 through which liquid can pass into and out of the bladderthrough an thereabove except when iiquid is forced into the bladderunder pressure.

The valve mecha 35b n incorporated in the screw plug M, the latter.being shaped to provide a cylindrical bore t?! therein, opposit ends ofwhich are closed by end plates 58 and (it, respectively, which havethreaded ports for the reception of the connections and 3.7., respectively.

There is slidably mounted within the bore til r a piston member 58,which is sealed with respect escapes through the jets i8.

to the bore 45? by a pair of sealing rings 55 and 52. At its right end,the piston 58 is sealed about a tubular neck 53, which extends into thepiston from the closure member 39, by a sealing ring 55. The closuremember to is sealed with respect to the bore G'd by a sealing ring 55.

A pair of puppets 56 and 51* are slidably mounted in a longitudinal bore58 within the piston 5d, the two poppets being urged apart by a lighthelical compression spring 59. Poppet 56 is adapted to seal against aseat 66 at the inner end of a neck bl projecting inwardly from theclosure member 58. The poppet 5? has two sealing surfaces, one adaptedto seal against a seat 62 on the inner end of the necl: 5t, and anotherone adapted to seat on a seat 63 in the piston 5%.

At its left end, the piston 59 is provided with a bushing 56 which sealswith the neck (it. The piston is normally urged into its right endposition, as shown, by a helical spring 65 compressed between the pistonand the left closure member it.

The complete system, including the unit 35, operates as follows, whenthe engine is to be started:

To start the engine, the starter switch 32 is actuated while thethrottle valve 2&- is ,closed. The rotor shaft it gradually accelerates,and the pump 22 is, of course, simultaneously accelerated, but duringthis initial operation, no fuel flows to the jets it because thethrottle valve 2 is closed.

However, the pump 22 delivers a gradually increasing flow of fuel, whichflows through the connection 36 and into the bore 58 of the piston 56,past the poppet 58, the latter being closed only by its light spring 59so that it functions as a check valve. The fuel entering the bore 58escapes therefrom past the valve seat es and flows through a passage 66into the bore "2-? and thence through the aperture id and the holes itinto the bladder 39, distending the latter against the pressure of theair thereabove. As the air is compressed, the pressure of the fuelwithin the bladder increases. Escape of fuel into the connection 3? isprevented at this stage of operation because the poppet 5? is seatedagainst the seat 62.

By the time the starting motor M has accelerated the rotor shaft it ofthe jet engine to a starting speed, considerable fuel pressure has beenbuilt up in the bladder 3d, and the operator then opens the throttlevalve 2%, whereupon fuel flows through the line it to the jets E8. Theline it is initially filled with air, and at first the fuel flowsthrough the line without building up much pressure because the air inthe line readily However, as soon as the linei is filled, and the fuelstarts flowin through the jets E8, the pressure in line it is suddenlyincreased because of the resistance to flow of the liquid fuel ofleredby the jets. This sudden rise in pressure in the line is is appliedthrough the connection at, and through a passage 67 in the end closuremember 69, to the right end of the piston 50, moving it to the left. Theleftward movement or the piston first closes the seat 63 against thepoppet 51 thereby preventing further flow of fuel through the bore 58past the seat 63. The final movement of the piston 50 to the leftcarries the poppet 51 with it, thereby opening the poppet away from theseat 62 and permitting fuel to flow from the interior of the bladder 39through the aperture 44, the bore 41, and the passage 66 to theconnection 31 and thence to the line l9.

Following initial opening of the-poppet 51 off the seat 62, fuel may besupplied to the line I9 from the accumulator at a pressure higher thanthat delivered by the pump 22, but any reverse flow of fluid from theaccumulator through line 31 and valve 24 back into the pump 22 isprevented by the check valve 23. A small vent 80 is provided between thebore 58 of the piston 50 and the annular recess 41 to permit escape offuel displaced from the bore'58 by the neck Bl as the piston 56 moves tothe left. A small leakage of fuel may occur through the vent 80 when thepoppet 51 is off its seat 62 but on seat 63, and thc pump is developinghigh pressure, but the vent 80 is so small that such leakage isinconsequential.

The net result of the operations described is that following filling ofthe line 19 the fuel stored under the pressure in the accumulator 35c isdelivered to the line 19 at high pressure even though the pump 22 maynot yet be running fast enough to maintain high pressure in the line i9.Fuel is, therefore, discharged from the jets H3 at a pressure suflicientto eilect proper atomization, insuring immediate ignition of the fueland starting of the jet engine. The latter thereupon accelerates to itsnormal speed, after which the fuel pump 22 is capable of maintainingfull fuel pressure on the jets without the aid of the accumulator.

During the normal operation of the jet engine, the piston 59 of the unit35 remains in its leftmost position because. the full pressure of thefuel in the connection 31 is applied to the right end of the piston,whereas the left end of the piston is exposed to atmospheric pressure bya vent 68 in the end closure member 48. Hence, open communication ismaintained between the connection 3?! and the bladder 39, past the seat62, through the passage 66 and the aperture 44.

In effect, the accumulator is therefore maintained floating on the line19. The pressure of the pump 22 in the inlet connection 35 is applied tothe left endof the poppet 51 and to the right end wall of the bore 58 inthe piston 59, urging the poppet 51 against the seat 63 and tending tomove the piston 50 to theright, but as long as the throttle valve 24 isopen, this pressure is unable to overcome the pressure acting againstthe right end of the piston 50, which has a substantially larger areathan does the bore 58 in the piston.

When the engine is to shut down, the operator closes the throttle valve26, which quickly reduces the pressure in the line H! and the connection31 to a low value, permitting the spring 65 to move the piston 56 intoits right end position, in which the poppet 51 closes on the seat 62 andopens off the seat 63. This prevents further escape of fuel from thebladder 39 out through the connection 31. However, the jet engineand'the pump 22 will continue to coast for a period following closure ofthe throttle valve 21, and as long as the pump delivers fuel, it willcontinue to flow through the connection 36 and into the bladder 39,where it will be stored to facilitate the next start.

I It will be apparent from the foregoing description that the use of theunit 35 in the system of Fig. 1 provides for the immediate supply offluid at high pressure to the jets I 8 following filling of the line ISin response to the opening of the throttle valve 24, so that immediateatomization and ignition of the fuel results. In addition to insuringpositive starting, the unit prevents the accumulation of unburned fuelin the engine prior to ignition.

Although the apparatus can be designed to function at various pressures,in an actual embodiment of the invention tested the pressures had thefollowing values: The normal air pressure in the accumulator shell 38when the bladder 39 was completely collapsed was between 60 and p. s.i.; the pump 22 was capable of developing between and 200 p. s. i. atthe starting speed of the jet engine; and was capable of developingapproximately 500 p. s. i. at full running speed. The spring 65 was soproportioned relative to the pressure areas of the piston 50 as to causethe piston to open the poppet 51 off the seat 62 at a pressure in theconnection 31 of between 15 and 26 p. s. i.

Although during normal operation of the engine the pressure in the linel9 and in the accumulator 35a may be as high as 500 p. s. i. thispressure drops quickly to zero value following closure of the throttlevalve 24, and the piston 50 is moved to the right by its spring 55 whenthe pressure in the connection 31 drops to about 10 p. s. i. Since theair pressure in the accumulator 35a is always at least 60 p. s. i., thebladder 39 will always be completely collapsed when the piston 50 isreturned to normal position by its spring 65. However, as previouslydescribed,- the engine continues to coast for some time followingclosure of the throttle valve 24, so that there is ample time toaccumulate substantial fuel in the bladder 39, following return of thepiston 50 to the right, and before the pump pressure drops appreciably.

Various departures from the exact construction described can be madewithout departing from the invention which is to be limited .only to theextent set forth in the appended claims.

We claim:

1. A valve device of the type described comprising: a body having aninlet port, an outlet port, and an accumulator port; first, normallyopen, valve means for communicating said inlet port with saidaccumulator port, second, normally closed, valve means for communicatingsaid accumulator port with said outlet port; and means responsive to arise in pressure in said outlet port above a predetermined valuerelative to the ambient pressure for opening said second valve.

2. A valve device of the type described comprising: a body having aninlet port, an outlet port, and an accumulator port; first. normallyopen valve means for communicating said inlet port with said accumulatorport, second normally closed valve means for communicating saidaccumulator port with said outlet port; and means responsive to anincrease of the pressure in said outlet port above a predetermined valuefor closing said first valve means and opening said second valve means.

3. A valve device of the type described comprising: a body having acylinder, an inlet port, an outlet port, and an accumulator port; pistonaeeaess imeansreciprocal in said cylinder and exposed to ambientpressure at one end and to pressure in said outlet port at the otherend; passage means in said body including a first valve seat forintercommunicating said outlet and accumulator ports; a poppet valvenormally closing said first seat; a second valve seat in said pistonmeans; means defining a passage from said inlet portthrough said secondseat to said accumulator port; the arrangement of said piston means andpoppet being .such that movement of said piston means in response topressure in said outlet port closes said second seat on said poppet andcarries the poppet clear of said first seat.

4. A valve device as described in claim 3 including a second poppetvalve seating against said inlet port, and spring means urging saidsecond poppet against said inlet port for permitting fiuid flow fromsaid inlet port into said body while preventing return flow through saidinlet port.

5. A valve device of the type described comprising: a body defining acylinder having an inlet port in one end thereof, an outlet port in theother end thereof, and an accumulator port in the side wall thereof; ahollow piston reciprocal in said cylinder and sealing with said inletand outlet ports, and with the side wall of said cylinder on oppositesides of said accumulator port, passage means communicating one end ofsaid piston with said outlet port; passage means communicating the otherend of said piston with the atmosphere; a valve seat within said piston,a poppet valve within said piston, spring means urging said piston intoone end position against the force of the pressure existent in theoutlet port; a poppet valve within said piston and spring means urgingit into sealing relation with said outlet port when said piston is insaid one end position; a valve seat in said piston in spaced relation tosaid poppet valve when said piston is in said one end position and saidpoppet is seated against said outlet port, said piston and outlet portdefining a chamber between said outlet port and said seat in said pistonnormally communicated through said seat in said piston with said inletport; said outlet port and said seat in said piston being so positionedrelative to said poppet valve that movement of said piston out of saidone end position by pressure in said outlet port first engages the seatin said piston against said poppet to prevent flow of fluid from saidinlet port through said seat in the piston, and thereafter carries saidpoppet clear of said outlet port to communicate said outlet port withsaid accumulator port.

6. A valve device as described in claim 5 includ ing an additionalpoppet within said hollow piston positioned back to back with respect'tosaid one poppet and adapted to seat against said inlet port, said springmeans being interposed be.- tween said two poppets for urging themapart.

7. In a fuel system for a combustion engine including a fuel-atomizingjet, a fuel pump driven by the engine, a fuel line connecting the pumpto the jet, a throttle valve in the fuel line, and

means for normally draining fuel from that portion of the fuel linebetween the throttle valve and said 'jets when substantially no pressureexists in the fuel line on the jet side of the throttle valve; anaccumulator; means normally connecting said accumulator to said line onthe pump side of said throttle valve; and means responsive to a rise inpressure in said fuel line on the jet side of said throttle valve abovea predetermined value for connecting said accumulator to said fuel lineon the jet side of said throttle valve.

8. A system as described in claim 7 including means responsive to saidrise in pressure in said,

fuel line on the jet side of said throttle valve above saidpredetermined value for substantially I preventing flow of fuel fromthat portion of the fuel line on the pump side of said throttle valveinto said accumulator.

9. A system as described in claim 7 including check valve means-forpermitting flow of fluid from that portion of said fuel line on the pumpside of said throttle valve into said accumulator while preventingreverse flow.

10. A system as described in claim 7 including means responsive to saidrise in pressure in said fuel line on the jet side of said throttlevalve above said predetermined value for substantially preventingfiow'of fuel from that portion of the fuel line on the pump side of saidthrottle valve into said accumulator, and check valve means for at alltimes preventing reverse flow from said accumulator into said fuel lineon the pump side of said throttle valve. 7

11. A system as described in claim 7 including means responsive to saidrise in pressure in said fuel line on the jet side of said throttlevalve above said predetermined value for substantially preventing flowof fuel from that portion of the fuel line on the pump side of saidthrottle valve into said accumulator, check valve means for at all timespreventing reverse flow from said accumulator into said fuel line on thepump side of said throttle valve, and check valve means in said fuelline adjacent said pump permitting fluid flow from the pump into theline while preventing reverse flow from said line back into the pump.

WALTER. C. 'IRAU'I'MAN. ALVIN A. MEDDOCK.

REFERENCES EDITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Taylor Dec. 5, 1944

